Design and fabrication of cost‐effective side‐stem micromechanical disk resonator with large capacitive gap

Abstract

A high-performance micromechanical disk resonator is developed for use in mass detection biosensors. The resonator is designed to facilitate easy and cost-effective fabrication by anchoring the disk on the side stems and increasing the capacitive gap size up to 4.75 µm. The designed disk resonator operates in an elliptic contour-mode at a resonance frequency of 5.971 MHz with a quality factor of 4272 in ambient air condition and 17 221 in a 600 Torr vacuum environment.Introduction: With interest in sensing and frequency filtering applications increasing, disk resonators that vibrate in an in-plane mode are highly promising. In these resonators, the air damping effect is significantly reduced and a relatively high quality factor (Q-factor) can be achieved in ambient air conditions. However, two key issues encountered in the fabrication of the disk resonator are the gap size between the disk and electrodes and the alignment of each part inside the resonator [1]. It is well known that narrowing the gap size requires much more complicated and expensive fabrication processes. Hao et al. developed a disk resonator with an ultra-narrow capacitive gap of the order of 100 nm by employing a complex HARPSS [2] process that required six lithography steps in total and a number of etching and deposition steps for wireless applications [3]. In the work reported in this Letter, we designed and fabricated a disk resonator with a large gap between the disk and electrodes and investigated its resonance behaviour. We confirmed that the high Q-factor achieved with low production costs makes the fabricated disk resonator suitable for biosensor applications.